1. Technical Field
The present disclosure relates to an optoelectronic device having a transition stack formed between the semiconductor layer and the substrate.
2. Description of the Related Art
The light radiation theory of light emitting diode (LED) is to generate light from the energy released by the electron moving between the n-type semiconductor and the p-type semiconductor. Because the light radiation theory of LED is different from the incandescent light which heats the filament, the LED is called a “cold” light source. Moreover, the LED is more sustainable, longevous, light and handy, and less power consumption, therefore it is considered as a new light source for the illumination markets. The LED applies to various applications like the traffic signal, backlight module, street light, and medical instruments, and is gradually replacing the traditional lighting sources.
Generally, the light extraction efficiency depends on the internal quantum efficiency and light extraction efficiency. The internal quantum efficiency can be defined as the opto-electrical conversion efficiency in the LED.
FIG. 5A illustrates the structure of a conventional light emitting device 10 which includes a transparent substrate 10, a buffer layer 1, a semiconductor stack layer 12 formed above the transparent substrate 10, and an electrode 14 formed above the semiconductor stack layer 12, wherein the semiconductor stack layer 12 comprises, from the top, a first conductive-type semiconductor layer 120, an active layer 122, and a second conductive-type semiconductor layer 124. At least one void 111 is formed inside the buffer layer 11.
However, as shown in the FIG. 5B, the conventional light emitting device 100 has a gray surface because of the void 111 inside the buffer layer 11, and the light transmission is decreased.